The newest flat-panel display is the field emission display (FED), which is developed at about 1980. The basic principles of light emission are the same for the FED and the cathode ray tube (CRT). Electrons are emitted from the cathode, and collide with phosphors coated onto the anode to generate light. What is different is the cathode itself. The CRT uses a point electron source, while the FED has an array of fine electron sources. In the CRT the electrons emitted from the source are deflected and scanned across the screen to produce the image, while in the FED several hundred cathodes are used for lighting each pixel. There is no scanning. Electrons from the cathodes sited directly below the phosphors of a pixel create the image, and as a result the panel thickness can be reduced to several millimeters. Further, while the CRT is a hot cathode device, i.e. it heats the cathode to produce electrons, the FED uses a cold cathode that generates electrons with a high voltage instead.
Although the FEDs are welcomed and are ramping up for volume production in the recent years, it is problematic the gates of the field emission devices will easily rub into the air during the transportation so as to induce electrostatic charges. When the charges are accumulated to a certain amount, the huge voltage differences between the gate and the tip structure of the field emission device, ranged from hundreds to thousands Volt, will be generated, causing the tip of the device to emit electrons. However, the tip cannot endure too much electric current in a short time and will burn itself up, resulting in dead pixels in the display. Therefore, how to design a protective structure of FED in order to prevent the tip of the field emission devices from damaging of large electrostatic discharging is becoming the most urgent problem to be overcome in the industry.
Please refer to FIG. 1, which is the schematic view showing the cross-section of the field emission device structure according to the prior art for solving the electrostatic discharge problem. In FIG. 1, a PN diode 13 is formed between the gate 11 and the tip 12 of the field emission device 1 to generate a path for electrostatic discharging. However, such structure can only be applied in passive triode field emission device, and can not be applied to other kinds of field emission device. Besides, in order to form the PN diode, a extra anneal process as well as a doping process of two extra mask steps are required, which generates more problems such as increasing mask cost, extra thermal budge, and decreasing throughput, and so on.